The size is based on the bust measurement. It looks like it's meant to fit loosely. Size 13 needles are a lot smaller than 19s, you should do a swatch and see if you like the result. At that point you can figure out the size issue. I think it will be a really tight knit on 13s unless you're an extremely loose knitter. You might do better to get needles in the right size.

I really like that pattern. If I make it for one of my girls, they'll both get to use it. My girls are my DD and her DD.

__________________~ GG
Happiness is catching that dropped stitch while it's still fixable..

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